A cross compound turbine-generator comprises a first generator which is rotated typically by the high and intermediate pressure portions of a steam turbine, and a second generator which is rotated by a low-pressure turbine portion. During acceleration of such a turbine-generator to its synchronous speed, the first and second generators are accelerated independently to a speed intermediate the turning gear speed and the synchronous speed, whereupon the generators are connected electrically. Then the shaft speed of the turbine-generator is increased from the intermediate to the synchronous speed.
The high-pressure portion of such a turbine-generator generally is connected to use superheat steam; in such case, steam that is exhausted from the high-pressure portion is reheated and returned for use by the intermediate and low-pressure portions. Typically a bypass line is connected across the high-pressure portion and another bypass line is connected across the intermediate and low-pressure portions. Such bypass lines permit a minimum passage of steam through the superheat and reheat sections of the steam source at times when the turbine steam flows are less than the minimum, thereby affording protection to the steam source from possible damage due to low-flow conditions.
In the event that a bypass system is connected across a turbine system as above described, the steam flow through the high-pressure portion and the flow through the intermediate low pressure portions may not be equal, at times when there is flow through the bypass lines.
If the steam source includes a high temperature gas-cooled nuclear reactor, hot coolant gas is discharged from the reactor and flows through a steam generator wherein reactor-generated heat is imparted to the flows of superheat and reheat steam. An auxiliary steam turbine means may be connected to use steam exhausted from the high-pressure turbine portion and its bypass line to drive a gas circulator, before such steam is reheated. The gas circulator propels the coolant gas through the reactor and the steam generator.
In case the steam source includes a high temperature gas-cooled nuclear reactor and an auxiliary steam turbine means is connected as above described, at least a minimum pressure of steam must be maintained at the exhaust of the auxiliary steam turbine means, for the proper and efficient operation of such means. As a result, steam that is discharged from the reheat section of the steam generator is at an elevated pressure when acceleration of the turbine-generator commences.
A proposed system for accelerating a cross compound turbine-generator commences acceleration by gradually opening the steam flow control valves associated with the high-pressure turbine portion, the steam flow control valve associated with the intermediate and low-pressure portions remaining fully open during the entire course of acceleration of the turbine-generator to its synchronous speed. At an intermediate speed, the low-pressure portion is accelerated by an equalizing steam flow until its rotational speed is equal to that of the high and intermediate pressure portions, whereupon the electrical generators are connected electrically. After such connection, acceleration continues under control of the steam flow valve associated with the high-pressure portion. The system apparently does not include the bypass lines associated with the turbine portions, as above described.
One limitation of the proposed system, in event of its application in a power plant wherein reheated steam is at an elevated pressure when acceleration commences, is that it permits an appreciable initial steam flow through the intermediate and low pressure turbine portions, making control of the shaft speed difficult, if not impossible. Another limitation of the system is that it permits an equal steam flow through the high, intermediate and low-pressure turbine portions, and therefore it is not adapted to a cross compound turbine with a bypass as above described, wherein the steam flows through the high and intermediate-low pressure portions need not be equal at times when there is steam flow the bypass lines.
There appears to be a need for an acceleration control system for a turbine system connected to a source of reheated steam that is at an elevated pressure when acceleration commences. Furthermore, there appears to be a need for an acceleration control system for use with a turbine and a bypass system wherein the steam flows through the turbine portions are controlled independently, for improved accuracy of acceleration control and for desirable heating and cooling of various turbine parts.
The description of prior art herein is made on good faith and no representation is made that any prior art considered is the best pertaining prior art nor that the interpretation based on its is unrebuttable.